Smokeless powder grains and method of making same



Patented Feb. 2, 1954 SMOKELESS POWDER GRAINS AND METHOD OF MAKING SAME William 0. Baker, Morristown, N. J.

No Drawing. Application January 11, 1950, Serial No. 138,073

3 Claims.

The present invention relates to the manufacture of smokeless powder grains and more particularly to the manufacture of such grains having greater mechanical strength than has heretofore been attained, making them more suitable for use as a rocket fuel.

A fuel commonly employed for the propulsion of rockets is smokeless powder, one of whose chief constituents is cellulose nitrate. The usual method of preparing the fuel charges for rocket propulsion consists of forming a plurality of grains of desired size and shape from a plastic mass of cellulose nitrate in a suitable solvent, said mass including the various other constituents of the charge, such as a nitrate salt and/or nitroglycerine or the like, dissolved therein or in suspension. In order to determine the ballistic characteristics of a rocket, it is necessary that each charge be controlled and uniform. Heretofore such determinations have been unreliable chiefly because of the fragmentation and fracturing of the grains during the burning of the fuel charge resulting in non-uniform combustion thereof.

It is therefore one object of this invention to provide smokeless powder grains that are superior to those heretofore produced, in that they offer greater resistance to fracture and fragmentation during ignition thereof, yielding determinable and reproducible ballistic characteristics of a rocket when employed as a propellant therefor.

Another object of the present invention is to j provide a smokeless powder grain of superior mechanical strength than has heretofore been known.

Another object of the present invention is to provide a smokeless powder grain comprising a plurality of laminae having oriented cellulose nitrate crystallites or molecules in each lamina, and alternatively having laminae with non-oriented crystallites interdispersed among the lam- .inae having oriented crystallites.

A further object of the present invention is to provide a smokeless powder wafer having uniaxial and/or uniplanar orientation of its cellulose nitrate crystallites.

A still further object of the present invention is to provide a smokeless powder grain comprising a mat of smokeless powder filaments, each filament having oriented cellulose nitrate crystallites, and alternatively being interwoven with other filaments whose crystallites are not so oriis to provide a process for producing uniaxial 2 and/or uniplanar orientation of the molecules or crystallites of cellulose esters such as cellulose nitrate, acetate, butyrate, acetate butyrate, acetate propionate and the like and other cellulose compounds.

A still further object of the present invention is to provide a grain comprising a plurality of sections of a cellulose compound, each section having uniaxial and/or uniplanar orientation of its cellulosic crystallites or molecules, and alternatively having sections with non-oriented cellulosic crystallites or molecules interdispersed among the sections having oriented crystallites or molecules.

Smokeless powder is usually formed of cellulose nitrate or a like cellulosic ester having suspended or otherwise contained therein various other constituents, such as nitrate salts and/or nitrolycerine or the like. According to the present invention grains of such a smokeless powder are made by forming a plastic composition of the cellulose nitrate by dissolving it in a suitable solvent such as acetone, alcohol, ether, or the like and introducing into said plastic composition the other desired constituents of smokeless powder. This composition is then extruded from a die or the like, the extrusion being carried out at high shear. The extrusion may be in the form of a sheet, ribbon, or filament or any other desired shape provided a high shear is maintained at the extrusion nozzle. The extruded form is then dried, While being maintained under tension along the line of extrusion during the drying step. This process results in substantially uniaxial orientation of the cellulose nitrate crystallites or molecules. The above process is equally applicable to other cellulose compounds such as acetate, butyrate, acetate propionate, acetate butyrate and the like.

In the above process, when substances whose structure includes crystallites are used, both crystallite and molecular orientation is obtained, but in the case of cellulose compounds not possessing crystallites, such as the mixed esters and highly plasticized cellulose esters such as compounded cellulose nitrate, the same desired properties are obtained by the molecular orientation in the absence of crystallites.

To obtain suitable orientation of the crystallites or molecules of the cellulose compound, the extrusion of the plastic mass in the above described process should be carried out at rates of shear greater than secondand at shearing stresses greater than 100 p. s. i. through orifices of /2 inch or less when the viscosity of the material being extruded is greater than 10 poises. The temperature in the drying step should be such that the extrusion rapidly attains a value of greater than poises. The tension maintained on the extrusion during the drying step is critical only for the brief time in which the viscosity is low and during this time should be relatively great, preferably near the breaking strength of the hot ribbon. The sufficiency of the shear during the extrusion process to produce the desired orientation can be determined by X-ray examination of the product, due to the X-ray scattering effect caused by the-orientation of the crystallites or molecules.

It has been found that cellulose nitra-te-and other cellulose compounds, having their crystallites or molecules oriented along an axis, present greater mechanical strength along the axis of orientation than can be obtained fromcommensurate samples of cellulose esters having random orientation oftheir crystallites or molecules. Since it is desirable, as discussed above, to .havegrains 10fsmokeless powder of high mechanical strength for thefuel charge for'rockets, the present invention contemplates in addik tion 'to the :foregoing process, the advantages to be derived therefrom in producing smokeless powder; grains from the product of the above process.

In .oneremhodiment of this invention derived from the above described process, a ribbon of smokeless powder, or .other mixture containing a cellulose ester or other-cellulose compound amenable to th above process, is formed'according to the foregoing process to produce uniaxially oriented crystallites or molecules therein. The dried 'ribbon'is .then divided into particles, sections or wafers ofuniform size. Several of these wafersare then laminated togethersuch that the axis of crystallite or molecularorientation of each lamina is preferably in a .difierentdirection from the axis of each other lamina. The resultant grain then hasgreater mechanical strength along the linesof these various axes than-can be obtained by-a random orientation of the crystallites or molecules.

The'lamination step may be carried out by any conventional process such'as by merely applying pressure to the stacked particles or by coating the surfaces of each particle'with a smallquantity of solvent, stacking the pieces, and then drying the product. Unoriented laminaemay, if desired, be .interdispersedamong the oriented laminae, sufiicient mechanical strength being supplied by the--latterto insure asufliciently strong grain.

In another embodiment of the present invention a filament of smokeless powder; orothermixture containing a =cellulose=ester or other cellulose compound amenable to the above process,- whose crystallites or molecules hav been-oriented according to the processdescribed above is produced, and then the filament'is divided'intoa piurality of shorter fibers or sections which .are"then formed intoa mat by any conventional process, the various fibers or sections being placed in the mat to provide for axes of orientation in a plurality .of directions. The grain formed thereby-is afforded greater mechanical strength than can be obtained from random orientation of the crystallites or molecules as in the previously described embodiment. A1so,. if desired, fibers whose crystallites or molecules are randomly oriented may be intermingled with the uni-axiallyorientedfibers. This embodiment may also :be appliedtov ribbons 'having oriented crystallites or molecules, as well as fibers, to produce a mat as here described.

A still further embodiment of th present invention involves an additional step to the above described process for producing uniaxially oriented crystallites, namely that a ribbon, sheet, or filament of cellulose nitrate, or other cellulose compound suchas acetate,.butyrat.e,i and the like, having uniaxially oriented crystallites may be given a uniplanar orientation of said crystallites in addition to uniaxial orientation by rolling or powder, or other cellulose compound amenable to the latter process, having its crystal1ites thus oriented may be divided into particles, sections, wafers, or fibersor the like, and if desired-various wafers may be laminated together or various fibers or ribbons may be matted togetherasabove described, thereby forming a smokeless powder grain having the axis of orientation ofvarious wafers or fibers on different linesfromzthose of other wafers or fibers, and thereby imparting to the wafer great mechanical strength along each of the said axes andalong the plane of orientation.

The uniplanar orientation above discussed may be accomplished independently of the uniaxial orientation, and whenso done is notdependent upon the existence of crystallites aszin the combined uniplanar and uniaxial orientation. The uniplanar orientation process :may, therefore, be applied to cellulose nitrate and other cellulose compounds such as acetate, butyrate, acetate butyrate, acetate propionate, and the-like to produce grains thereof, as above described, having great mechanical strength ;due to the uniplanar orientation of the molecules or crystallites thereof.

It is thus apparent that by use of any cf the foregoing embodiments of the present inventiona smokeless powder grain may be formed suitable for use as a motive fuelcharge for rockets, and having such mechanical strength as substantially to eliminate the fragmentation or fracture' of the grain due to the shock waves that traverse the charge on ignition, thereby imparting-reproducible and predictable ballistic characteristics to the rocket flight.

The embodiments of the present invention herein described ar only illustrative thereof. Other embodiments and modifications of-tn-e present invention within the spirit-and scope of the appended claims udll be *apparent'to those skilled in the-art.

What is claimed is:

1. The process of producing'a smokeless powder grain comprising the steps'of extruding a plastic smokelesspowder composition under high shear, drying said extrusion, maintaining said extrusion under tension while drying, thereby imparting a substantially uniaxial orientation to the cellulosic crystallites thereof, comprising the Product thus formed to from one-third to one-fifth its thickness, thereby imparting a substantiallyunh planar orientation to the cellulosic crystallites of said product in addition to the uniaxial orientation, dividing said product into particles or sections, and uniting said particles or sections to form said grain with a plurality of axes of cellulosic crystallite orientation.

2. The process of producing a grain containing an ester chosen from the group consisting of cellulose nitrate, cellulose acetate, and cellulose butyrate comprising the steps of extruding a plastic composition of the cellulose ester under high shear, drying said extrusion, maintaining said extrusion under tension while drying, thereby imparting a substantially uniaxial orientation to the cellulose ester crystallites thereof, compressing the product thus formed to from one-third to one-fifth its thickness, thereby imparting a substantially uniplanar orientation to said crystallites of said product in addition to the uniaxial orientation, dividing the resultant product into particles or sections, and uniting said particles or sections to form said grain with a plurality of axes of orientation of said cellulose ester crystallites.

3. The process of producing a grain containing a cellulose ester having a crystallite structure comprising the steps of extruding a plastic composition of th cellulose ester under high shear, drying said extrusion, maintaining said extrusion under tension while drying, thereby imparting a substantially unia-xial orientation to the cellulose ester crystallites thereof, compressing the product thus formed, thereby imparting a substantially uniplanar orientation to the cellulose ester crystallites of said product in addition to the uniaxial orientation, dividing the resultent product into particles or sections, and uniting said particles or sections to form said grain.

WILLIAM O. BAKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,784,758 Sheppard et al. Dec. 9, 1930 1,808,998 Sheppard et a1 J1me 9, 1931 2,000,013 Dreyfus et al May 7, 1935 2,067,025 Schmidt Jan. 5, 1937 2,320,243 Mackey May 25, 1943 

1. THE PROCESS OF PRODUCING A SMOKELESS POWDER FRAIN COMPRISING THE STEPS OF EXTRUDING A PLASTIC SMOKELESS POWDER COMPOSITION UNDER HIGH SHEAR, DRYING SAID EXTRUSION, MAINTAINING SAID EXTRUSION UNDER TENSION WHILE DRYING, THEREBY IMPARTING A SUBSTANTIALLY UNIAXIAL ORIENTATION TO THE CELLULOSIC CRYSTALLITES THEREOF, COMPRISING THE PRODUCT THUS FORMED TO FROM ONE-THIRD TO ONE-FIFTH ITS THICKNESS, THEREBY IMPARTING A SUBSTANTIALLY UNIPLANAR ORIENTATION TO THE CELLULOSIC CRYSTALLITES OF SAID PRODUCT IN ADDITION TO THE UNIAXIAL ORIENTATION, DIVIDING SAID PRODUCT INTO PARTICLES OR SECTIONS, AND UNITING SAID PARTICLES OF SECTION TO FORM SAID GRAIN WITH A PLURALITY OF AXES OF CELLULOSIC CRYSTALLITE ORIENTATION. 